1. Field of the Invention
This invention relates to a button type air depolarized battery provided with a porous fluoroplastics membrane having low air permeability adjacent to the air hole and to a method of making such porous fluoroplastic membrane having low permeability.
2. Prior Art
Air depolarized batteries, which use oxygen in the air as the positive active material and zinc as the negative active material, is enjoying extended use due to reduced environmental pollution when discarded.
In FIG. 1, the general construction of a button type air depolarized battery is shown. As shown, zinc 1 is contained in a negative electrode case 2, which is closed by a positive electrode case 4 with gasket 3 in between. A separator 5 separates an air depolarized electrode 6 and zinc negative electrode 1. The air depolarized electrode 6 is in contact with a porous fluoroplastic membrane 7, which is layed inside the positive electrode case 4 having an air hole 8, with a diffusion paper 9 between membrane 7 and positive electrode case 4. Air hole 8 is closed with a sealing paper 10, which is to be removed before usage.
The function of the porous fluoroplastic membrane 7 is to control the supply of oxygen containing air to the inside of the battery, and to prevent the leakage of the electrolyte.
The button type air depolarized battery has the air holes 8 closed by sealing paper 10. When the sealing paper is torn off, the air holes are open and air is supplied through them to electrode 6, thus allowing the battery elements to react and produce an electromotive force.
As the method of manufacturing porous fluoroplastic membrane, the following two methods were known so far: